The present invention relates to a steering wheel and airbag combination. The combination comprises a steering wheel armature and separate hub plate having a structure for attachment to a steering column shaft. The invention also relates to a method of forming a modular steering wheel and airbag combination and a method of assembling a modular steering wheel and airbag combination.
Before the introduction of airbags, steering wheel assemblies could be easily attached to a steering column shaft. Access to the column shaft through a steering wheel assembly was made through the hub of the steering wheel assembly from a front face of the steering wheel assembly.
Airbag assemblies for a driver of a vehicle are typically located on the hub of a steering wheel assembly. Thus, access to a steering column shaft through the hub of a steering wheel assembly has become more difficult. Current methods of attaching a steering wheel and airbag assembly to a steering column shaft require a two step process. A steering wheel assembly is initially attached to a steering column shaft. An airbag assembly is then attached to the steering wheel assembly.
This two step, two-component assembly of steering wheel and airbag assemblies requires a great deal of time and has increased labor costs. Additionally, automobile manufacturers typically obtain the steering wheel assemblies and airbag assemblies from separate suppliers. Due to the two step assembly, the airbag and steering wheel have separate covers. The colors and textures of the two covers must be evenly matched to assure customer satisfaction. Even so, matching the colors exactly has proven difficult.
Another major problem of the current steering wheel and airbag assemblies is the theft of airbag assemblies. Because airbag assemblies are very expensive and can be easily removed from a vehicle, theft of airbag assemblies has risen dramatically. The prior art has made various attempts to address these problems but has been unsuccessful.
The modular steering wheel and airbag combination of the present invention includes a steering wheel armature and a separate hub plate. The separate hub plate provides a unique way of assembling the steering wheel and airbag combination. An airbag assembly is attached to a hub plate to form a hub plate sub-assembly. The hub plate sub-assembly is then attached to a steering wheel assembly including the steering wheel armature. A structure for securing the steering wheel and airbag combination is accessible from a rear face of the combination. The combination is then positioned over steering column shaft and then secured to the steering column shaft.
One aspect of the present invention includes a steering wheel armature which includes an upper rim portion and structure for attaching the upper rim portion to the hub plate. Preferably, the upper rim portion is essentially circular. The structure may include a plurality of spokes or ribs which extend from the upper rim portion of the steering wheel armature. Bolts attach the hub plate to the armature. In one embodiment a wedge lock is formed between the steering wheel armature and hub plate. The spokes include a seating surface at the opposed end of each spoke and the hub plate includes a plurality of tapered nubs which are forced into the seating surfaces. When the bolts secure the hub plate to the opposed ends of the spokes, a wedge lock is formed between the nubs and seating surfaces. The wedge lock is sufficiently strong that the bolts become unnecessary for retaining attachment after the bolts are originally driven.
The steering wheel armature also preferably includes a lower ring portion which connects the opposed ends of the spokes. The ring provides structural integrity and support to the steering wheel armature. In one embodiment, the hub plate conforms to the size of the ring portion. A plurality of fingers or pins are disposed adjacent lateral edges of the hub plate. A plurality of bores are disposed at lateral edges of the ring portion. Inner and outer airbag covers of the airbag assembly include interlocking tabs, each having a hole. The tabs are disposed between the ring portion and hub plate. The fingers pass through the holes and terminate in the bores in the ring portion. This provides a retaining feature to maintain the inner and outer airbag covers of the airbag assembly essentially within the combination during activation of the airbag component during, for example, a collision.
Another aspect of the invention includes an airbag retaining ring which facilitates assembly of the steering wheel and airbag combination. In a hub plate sub-assembly, an airbag inflator is disposed on a hub plate. An airbag envelope is disposed over the airbag inflator. During activation of the airbag inflator, a significant gas pressure inflation force is exerted to the airbag envelope. A retaining ring is provided as part of the airbag envelope which is disposed around a base of the airbag inflator. The ring is attached to the hub plate with a plurality of fasteners. In a preferred embodiment, a lip extends from a base of the inflator and is disposed between the hub plate and retaining ring. The structure of the hub plate is optimized to take advantage of the retaining ring structure.
The steering wheel and airbag combination also includes an attachment structure for securing the combination to a steering column shaft. The structure is accessible from a rear face of the combination remote from an outer covering facing the driver of a vehicle, preferably from an angle perpendicular to the steering column shaft axis. The attachment structure may include a worm gear and a complementary gear. The attachment structure preferably provides primary, secondary and tertiary retention features.
In one embodiment, the complementary gear is a helical gear having a gear portion, with angled teeth, and a threaded shaft extending from a face of the gear portion. The worm gear is adapted to drive the helical gear to secure the combination to the steering column shaft, thereby providing a primary retention feature. Typically, worm gears are used with gears having curved teeth. In those combinations, the gear may not move axially relative to the worm gear. With the helical gear some relative axial movement is possible. To remove the steering wheel, the worm gear may be reversed to draw the helical gear axially away from the steering column. The helical gear assists in forcing the hub plate away from the steering column shaft by impinging on the back of the inflator. This assists in breaking the xe2x80x9cwedge lockxe2x80x9d between the hub plate and steering column shaft, described below. The friction and gear ratios between the worm gear and helical gear provide a secondary retention feature which prevents the combination from disengaging from the steering column shaft.
The attachment structure may also include a collar extending from a rear face of the combination disposed around the threaded shaft which protrudes from the rear face. The steering column shaft includes a threaded bore and a tapered outer surface. The threaded bore receives the threaded shaft of the helical gear. An inner surface of the collar engages the tapered outer surface of the steering column shaft. The inner diameter of the collar is less than the maximum width of the tapered steering column shaft. Thus, as the combination is secured onto the steering column shaft, a wedge lock is created between the collar and steering column shaft, thereby providing a tertiary retention feature. This tertiary retention feature provides the most secure attachment between the combination and the steering column shaft of the primary, secondary and tertiary retention features.
Alternative embodiments of the structure for securing the combination to a steering column shaft include a collar having a threaded inner surface, where the steering column shaft includes a threaded outer surface. Another alternative embodiment includes a collar extending from the opposed face of a hub plate with a tooth disposed on an inner surface of the collar, where the steering column shaft includes a circumferential, spiral groove. In either embodiment, the combination is secured to a steering column shaft by placing the combination over a steering column shaft and rotating the combination to a predetermined stop position. A locking bolt is then inserted into a threaded bore essentially perpendicular to the collar.
A method of forming a modular steering wheel and airbag combination is also disclosed. A steering wheel armature is provided. An outer airbag cover may be disposed in a center area appurtenant to the steering wheel armature. A R.I.M. urethane outer covering is disposed around the upper rim portion and spokes of the steering wheel armature and the outer airbag cover reinforcement/substrate. In an alternative embodiment, an outer resin covering and the inner airbag cover are simultaneously molded in an injection mold using a compatible resin. A hub plate sub-assembly is also assembled including a worm gear and helical gear, airbag inflator, airbag envelope and inner airbag cover. The hub plate assembly is disposed within the outer airbag cover and secured to the ring portion of the steering wheel armature. The combined hub plate and steering wheel is then attached to the vehicle.